Do you know this game ?
The Amiga version exist really ? Or it was only developped for Atari ?

No Amiga version exists of this online game- it was only developed for the C64 AFAIK.

Incidentally, one of the Habitat developers (Chip Morningstar) coined the term 'avatar' while writing it. He took the word from an Indian dialect and used it as a general term for the characters in the game.